This blog discusses current weather, weather prediction, climate issues, and other topics

Saturday, January 22, 2011

Where is La Nina?

A question that several of you are asking is "Where is La Nina"?

Where are all the deep snows in the mountains that are often associated with it?Or the big snows over the lowlands?Is winter over?

So what is the situation now?

But before I go into that, let me remind all of you about Weatherfest tomorrow (Sunday) from 12-4 PM at the WA State Convention Center. Designed for K-12 folks, but fun for everyone, there will be booths for many weather related groups and agencies, local weather celebrities (like Jeff Renner, and Steve Pool), demonstrations, and lots of freebies. No admission fee.

Back to La Nina. Some facts:

(1) We are clearly in a moderate La Nina and will continue to be in one for the remainder of the winter.(2) La Ninas are associated with above-normal precipitation and below-normal temperature over the region (the latter generally after Jan 1). They also tend to bring above normal snowpack in the mountains and above normal snow over the lowlands.

But keep in mind this is all probabilistic. The dice are weighted towards these things, but they don't have to happen. There are La Nina years where snowfall has been below normal for example.

(3) During moderate to strong La Nina years there are typically less MAJOR floods and windstorms and the atmospheric flow is highly variable, often with major ridges (high pressure areas) in the eastern Pacific.

So how is the snowpack doing? Here is the % of normal water in the snowpack around the western U.S. Below normal for the WA Cascades, near normal over Oregon, and above normal over the Olympics. Well above normal in the Sierras. Not a typical La Nina pattern.

What about temperature and precipitation over the lowlands this month? Temperature has been highly variable--with swings from much colder than normal to warmer than normal periods. The variability is La Nina like, but the net temperature is not below normal.Precipitation has been slightly above normal--the result of extended dry periods and short periods of heavy rain (and warm).However, there have been few periods of heavy precipitation and cold..and thus snow has been lacking.

So is this going to be a snow bust La Nina year? Folks, it is too early to tell. The mountain snowpack tends to increase into March--often reaching its peak in late March or even early April. Here is the current and typical snowpack for the Seattle watershed--the peak is around April 1.

And you can see we are below normal at this point, but the climatological maximum is not until early April.

For the lowlands, we are now past the peak of the big snow events and there is nothing in our immediate future. But the lowlands can get snow events into early March...so we have a little over a month left to give to enjoy the white stuff at low levels (see plot of Seattle historic snow events)

Finally, this week we will have a "dirty ridge" over us initially, one that will allow some precipitation into at least the northern part of the state. Current model runs indicate amplification of the ridge, and complete drying, by mid-week.

No major storms in the offering.

This benign weather report is clearly due to the presence of thousands of meteorologists in town for the annual meeting of the American Meteorological Society. The weather gods know not to cross us.

PS: Please considering contributing to supporting our local efforts and the department.. see links to the upper right and something I added today:

This current weather pattern appears to be "locked in"--very similar to January-February 1984, another La Nina winter.Cold or snowy weather did not return that winter.However, for the snow lovers out there, there is a chance that the upper level ridge may repositon itself (20-30 degrees of longitude) further west,causing a colder north or northwest flow. Historically,this sometimes has happened during past La Nina events.

It also will be very interesting to check the CPC website on the 31st to see if the current February forecast of below normal temps and above normal precip has been revised.

So, Cliff ~ We usually fall into a "nuetral" phase between La Nina and El Nino years. I know we didn't have a nuetral phase this time. But...I've always heard that flooding and wind storms and sometimes snow can be much worse in nuetral years than La Nina years. I was wondering if the 2011/12 winter will be a nuetral and if what I've heard is or is not correct about it being worse.

I know you can't forecast the future using past occurrences. But old data shows that a stretch of strong la nina, 1954 to 1957, Seattle's only snow (54-55), occurred in February and March. 16 inches. Then winter of 55-56 is legendary across the entire PNW.

Hopefully, folks will not try and connect global climate change with the atypical LaNina pattern this year. It is a convenient pattern of thought, but scientifically unverifiable. Good analysis, Dr. Mass and also from climo man who brought up the LaNina event of 1984.

In looking ahead, hopefully there will be more of a summer than last and also a pickup in the snowpack in February and March. I predict there will be some upcoming LaNina "fingerprints" on the weather of winter and possibly early spring 2011.

I will be careful to state that I don't think there is any proof at all that this atypical La Nina is being affected by very out of the ordinary climatic patterns this year.

But I will say that the front page of the NYT has an article outlining the very bizarre mildness of the arctic this winter, and how what is normally arctic air is intruding far to the South into both the Eastern US and Europe.

http://www.nytimes.com/2011/01/25/science/earth/25cold.html?hp

With the broader jet stream being chaotically out of its pattern in the Eastern hemisphere, I just hypothesize that our La Nina's broader pattern may be influenced by this.

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"(3) During moderate to strong La Nina years there are typically less MAJOR floods and windstorms and the atmospheric flow is highly variable, often with major ridges (high pressure areas) in the eastern Pacific."

I have especially noticed the lack of windstorms this winter, particularly of the southerly variety. While we have had a few easterly wind events and Fraser Outflows, those tend to be localized in nature rather than widespread. The classic windstorm scenario with the low pressure making landfall across Vancouver Island has been in short supply. I am hoping for a neutral ENSO condition next fall and winter, as there is nothing I enjoy more than a good windstorm.

The mountains definitely need more snow. Things weren't looking so great up at Crystal this weekend - lots of warning sticks out. At least they won't be losing ground this week - that rain was a killer.